The vertebrae in a patient's spinal column are linked to one another by the disc and the facet joints, which control movement of the vertebrae relative to one another. Each vertebra has a pair of articulating surfaces located on the left side, and a pair of articulating surfaces located on the right side, and each pair includes a superior articular surface, which faces upward, and an inferior articular surface, which faces downward. Together the superior and inferior articular surfaces of adjacent vertebra form a facet joint. Facet joints are synovial joints, which means that each joint is surrounded by a capsule of connective tissue and produces a fluid to nourish and lubricate the joint. The joint surfaces are coated with cartilage allowing the joints to move or articulate relative to one another.
Diseased, degenerated, impaired, or otherwise painful facet joints and/or discs can require surgery to restore function to the three joint complex. Damaged, diseased levels in the spine were traditionally fused to one another. While such a technique may relieve pain, it effectively prevents motion between at least two vertebrae. As a result, additional stress may be applied to the adjoining levels, thereby potentially leading to further damage.
More recently, techniques have been developed to restore normal function to the facet joints. One such technique involves covering the facet joint with a cap to preserve the bony and articular structure. Capping techniques, however, are limited in use as they will not remove the source of the pain in osteoarthritic joints. Caps are also disadvantageous as they must be available in a variety of sizes and shapes to accommodate the wide variability in the anatomical morphology of the facets. Caps also have a tendency to loosen over time, potentially resulting in additional damage to the joint and/or the bone support structure containing the cap.
Other techniques for restoring the normal function to the posterior element involve arch replacement, in which superior and inferior prosthetic arches are implanted to extend across the vertebra typically between the spinous process. The arches can articulate relative to one another to replace the articulating function of the facet joints. One drawback of current articulating facet replacement devices, however, is that they require the facet joints to be resected. Moreover, alignment of the articulating surfaces with one another can be challenging.
Accordingly, there remains a need for improved systems and methods that are adapted to mimic the natural function of the facet joints.
Traditional spine fusion may result in early degeneration at adjacent spine levels due to increased loading and compensation. This may result in subsequent surgeries to fuse additional levels. Stabilization using more dynamic rods with traditional pedicle screw instrumentation may improve surgical outcomes and reduce additional surgeries for adjacent level degeneration.
PCT Patent Application WO02/17803 (Rivard I) and U.S. Pat. No. 6,554,831 (Rivard II) disclose a mobile dynamic implantable spinal apparatus designed with an aim towards treating scoliosis. Rivard I and II disclose a system including at least one correcting rod, at least one fixed bracket, at least one mobile carrier. The correcting rod is described as a scoliosis rod. Scoliosis rods are constructed of metallic materials, such as CoCr, Ti, and stainless steel. Such rods must be manufactured from very stiff materials in an effort to maintain correction.
U.S. Pat. No. 5,672,175 (Martin) discloses a dynamic spinal orthotic implant that preserves some of the physiologic spinal motion. The construct also includes a rod that is used to correct a lateral deviation or scoliosis curve.
US Patent Publication 2004/0049190 (Biedereman I) discloses a dynamic system utilizing two bone anchors, a rod, and a spring. One of the anchors is fixed to the rod, one anchor slides with respect to the rod, and the spring between them exerts a force from the fixed anchor to the sliding anchor.
US Patent Publication 2007/0233085 (Biedermann II) discloses a dynamic stabilization device utilizing a rod that is elastomeric and stretches rather than slides.
U.S. Pat. No. 7,326,210 (Jahng) discloses a dynamic stabilization device using a rod, elastomers, and a sliding sleeve.